Motor control circuits



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JEFFERSON R- WILKERSON;

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Filed July 24. 1942 INVENTOR J EFF E RSON R WI LKERSON;

Hls ATToRNEv Patented Sept. 7, 1948 MOTOR CONTROL CIRCUITS Jeierson R. Wilkerson, Bayside, N. Y., asslgnor to The Sperry Corporation, a corporation of Delaware Application July 24, 1942, serial No. 452,239

so claims. (ci. 31a-31) The present system is concerned with the art including apparatus for modifying control signals to produce time integrals or derivatives thereof, as in the control of ponderable objects and, more especially, the non-lagging, non-hunting control of such ponderable objects.

In control systems of the present type, such as follow-up systems or servo systems controlling heavy objects, or automatic pilots for aircraft or ships, wherein a large ponderable object is to be controlled from a control signal of relatively small magnitude and low power, it is well known to amplify these control signals in power and/or magnitude to provide a suiiicient controlling eiect to actuate a servo mechanism to control the ponderable object, as desired. In order to avoid hunting and lagging eiiects, it is also known to modify the control signal by the addition of components corresponding to the rate of change and also to higher time derivatives of the control signal. Such systems, however, are subject to the disadvantage that any variation in the amplifying apparatus, such asi is necessarily caused by uctuations in power supply voltage, variations in vacuum tube characteristics due to aging or hard usage, etc., have a corresponding and definite effect upon the output of the control circuit actuating the servo mechanism.

According to the present invention', improved control signal amplifying and rate deriving circuits are provided, `suitable for use in such ponderable object control systems, whereby vthe harmful eiects of variation in the control signal ampliiicatlon and rate signal generation are greatly minimized and substantially eliminated. In the present invention this may be performed by the use of a feed-back amplifierl in which the output signal is degeneratively fed back to the input after modification in such manner as to produce the required combination of control signal and its time derivatives in the output circuit. As will be seen, this is most easily done by the incorporation of suitable integrating circuits in the negative feed-back path.

Accordingly, it is an object of the present invention to provide improved'apparatus for controlling a ponderable-object in response to a relatively weak control signal.

It is another object of the present invention to provide improved rate deriving and control circuits for use in controlling ponderable objects,

substantially independent of the amplification produced in these control circuits.

It is still another object of the present invention to provide improved integral and rate deriving circuits in which the eilects of non-linearity or fluctuations in the amplification of thermionic amplifiers associated therewith are greatly minimized and substantially eliminated.

I It is a further object of the present invention to provide an improved derivative or integral deriving circuit by the use of negative feed-back ampliers.

It is still another object of the present invention to provide improved rate deriving circuits and amplifying means including an integrating network in a negative feed-back path for said amplifier, whereby variations in the amplification of said amplifier due, for example, to tube variations or power supply variations, are rendered ineiiective in the output thereof.

Other objects and advantages will become apparent from the speciiication, taken in connection with the accompanying drawings in which,

Fig. 1 is a schematic'representation of an exemplary system embodying the present invention.

Fig, 2 shows a schematic block diagram of the improved circuit of the present invention.

Figs. 3 to 13 show various types of translating circuit which may be used with the system of Fig. 2` to provide time derivative outputs.

Figs. 14 to 2l show other types of translating circuits useful in the system of Fig. 2 to provide time integral outputs.

Figs. 22 to 25 show modifications of the circuit of Fig. 2.

Figs. 26 to 28 show specific detailed embodiments of several forms of rate amplifiers of the form of Fig. 2. y

In Fig. 1 there 'is shown a schematic diagram of a control system for a ponderable object, shown for illustration purposes as a conventional type of follow-up system, comprising a sensitive controlling element, such as a control shaft II, whose low-power angular displacement it is desired to reproduce as a corresponding and preferably equal angular displacement of an output shaft I2 which actuates a ponderable object (not shown). For this purpose, a pick-oli? I3 is provided adapted to produce a signal indicative of the relative displacement between control shaft II and output shaft I2.

In the present instance, this pick-.olf is shown as of the conventional three-legged magnetic type comprising a three-legged core I4 carried on an arm I6 fixed to the output shaft I2. The center leg of core I4 carries an energizing winding energized from any suitable source of alternating current. The outermost legs of core Il also carry windings I5 which are connected in ,voltage output upon departure from this pre determined relative position, corresponding in phase-sense and magnitude to the sense and magnitude of the relative displacement between the control shaft II and the output shaft I2. Such pick-offs are well known in the art and need not be further described here.

The output of pick-oir I3 is fed to a control circuit I1 including a phase-sensitive amplifier, which may be of any conventional type, adapted to produce in its output a reversible-polarity di- I rect-current signal corresponding in magnitude and polarity to the magnitude and phase-sense of the pick-off signal, and, accordingly, to the magnitude and sense of relative-displacement between the control shaft II and output shaft I2.

It will be clear from what follows that the present system need not be restricted to this type of control-signal-producing means but that any type of pick-off, adapted to produce a control signal, either alternating or unidirectional, representing the sense and magnitude of the relative displacement between control shaft II and the output shaft I2, may beused. In addition, the present invention is not restricted only to follow-up systems, but also includes systems where a ponderable object is controlled by a weak signal corresponding to deviation of the object from a desired condition. One such system is an automatic pilot for aircraft or ships Where the steering of the craft is controlled from a weak signal derived from a compass, gyro or other orientation-maintaining instrument. In the aircraft pilot, the attitude of the craft in pitch and roll may be thus controlled by the signal derived from a gyra-vertical or other verticalmaintaining instrument. Other types of systems include remote control or servo mechanisms, where the position or speed of a ponderable object is controlled in correspondence with a remotely produced low power signal. Many other uses of the present system are also possible, as will be seen, wherever the character of a con- `trol signal has to be modified by the addition of components corresponding to time derivatives or time integrals of the time variation of the control signal.

The output of phase-sensitive amplifier I1 is generally fed in prior art systems to a rate circuit which includes suitable weil-known circuits for adding to the control signal various components representing iirst and/orI higher time derivatives thereof, and for amplifying such signals. The outputV of the rate circuit then serves to actuate a servo device 2|, which may be of any type, adapted to produce an output motion corresponding to the control signal input thereto. Generally speaking, servo 2| will be a device' capable of substantial power output in order to suitably control whatever ponderable object may be connected to output shaft I2.

The output of servo 2I is suitably coupled to output shaft I2 and is connected thereto in such sense as to restore output shaft I2 to correspondence with control shaft II and thereby diminish the control signal derived from pick-od I 3, which, in the case of a follow-up system such as here shown, may be termed an error" or "displacement signal. By suitably proportioning the components of the signal voltage controlling the servo 2l, which components usually represent the relative displacement between control shaft II' and output shaft I2, the rate of change of this displacement and the second derivative of this displacement (which may \be considered to be the relative acceleration of the two shafts in the present illustration) as well as any desired higher derivatives, it is possible to cause output shaft I2 to follow the angular motion of control shaft II substantially without hunting or oscillating and without lag. The first time derivative of the control signal will be hereinafter termed a rate signal.

Such systems as that shown in Fig. l are well known in the art, as exemplified by the following Hull.- Patent Nos. 2,068,490, 2,088,654, and 2,233,415 for Positional control systems. However, in all of the prior art devices using such rate circuits, the'output voltageof the rate circuit is greatly decreased in magnitude in comparison tov theY input voltage representing the control signal. Therefore, it is necessary to provide a large amount of additional amplification for the combined derivative and lcontrol signals in such prior art devices. Such ampliers, however, are subject to well known defects and variations in their amplification properties, due primarily to non-linearity of their amplification characteristics and variations in gain, such as due to fluctuations in power supply voltage, and to variations in tube characteristics because of age, usage. etc. tion cause wide variations in the output of the rate circuit, and have a correspondingly harmful effect upon the desired operation of the servomotor controlled thereby.

These defects of the prior art device may be substantially overcome by the present invention. Referring now to Fig. 2, there is shown a schematic diagram of the improved rate circuit of the present invention, which may be embodied in the control circuit of Fig. 1. This circuit comprises an amplifying device 22 whose output voltage having instantaneous value e@ is fed through a translating circuit 23 to be later described to produce an instantaneous feedback voltage er which is added to the instantaneous control voltage e1 input to the amplifier 22.

Let it be assumed that the instantaneous ratio of output voltage e0 to input control voltage e1 with zero feedback voltage er is equal to u, and that the ratio of the instantaneous value of feedback voltage ef to the voltage input of translating circuit/23, namely, et, is given by which may be termed' the instantaneous gain of the feedback circuit 23. Accordingly, the operation of amplier 22 may be described by the equation by using the relationship between er and en, where A is the overall instantaneous gain of the improved rate circuit; that is, A is the instantaneous ratio of output to input voltages of the entire system.

If now the characteristics of amplifier 22 and translating circuit 23 are so chosen that a is very much larger than unity, the quantity 1 in the de- These variations in amplificanominator of the preceding equation will be negligible in comparison to the quantity m3, and the preceding Equation 2 may be rewritten as e.= 3) If we substitute for e its value it will be seen that et-ef (4) In other words, for the assumed condition to hold, it is necessary that the feedback voltage be instantaneously of substantially the same magnitude as the control signal el. This may be accomplished by a suitable design of the translating circuit 23, whose characteristics `have not yet been described,

If' we assume that the feedback voltage er derlved from the output voltage e0 by action of the translating circuit 23 has a voltage Wave form which is an arbitrary function F- of the output voltage en we may write e;=F(e) (5) From Equation 4 this becomes ea-Fo) (6) eoF-l (el) (7) where the latter equation merely means that el will bear the same functional relation to e0 as er does to ee. Stated diierently. eo is related to el by a functional relation which is the inverse oi' that by which e: is related to e0, so that e1 will be the same function of e0 `as ef is of e0.

Accordingly, th'e above analysis shows clearly that the use of a translating circuit in the negative feedback path of an amplier having high amplification tion (y.) with respect to the attenuaof the translating circuit will produce an output from the system having a wave shape which is the inverse function of the wave shape produced by the translating circuit from the Voltage input t0 this translating circuit. For example, if it is desired to produce an output voltage e0 from the system which is proportional to the time derivative or rate of change of the input voltage el, then by the above analysis the translating circuit 23 should produce a feedback voltage er' which is the inverse derivative or actually the integral of the voltage eo input to the translating circuit 23. This may easily be shown in the following way:

Assume that as is desired. But from (4),

el-ef (9) since the minus -sign may eiectively be disregarded as it merely connotes a reversal of polarity as by an interchange of terminals. Accordingly,

v ,glf I edt (10) or integrating both sides of this last equation,

' ef=fedt (11) duce an output voltage er'which is the inc tegral oi e with respect to time. Such integrating circuits are well-known in the art, and therefore. may be used directly as the translating circuit 23 to produce a signal output e which is the rate of change ci the input signal el. v

Figs. 3-21 show various types of translating circuit 2l for use with the system of Fig. 2. It is to be understood in all of these circuits that a 1, so that Equation 4 is valid.

Thus, Fig. 3 shows a series circuit comprising a resistor R and condenser C, the feedback voltage er being derived from the volt drop across conwhich shows that the translating circuit 23 must operate upon its input voltage eo to prodenser C. Ii i is the current flowing through R and C, then yfeed-back path.

jFig. 4 shows another translating circuit similar in eiect to Fig. 3. but comprising a coil having inductance L in series with a resistance R.. the feedback voltage e: being derived from the volt-drop across resistor R. Here it may be shown that again yielding a combination of control signal el and its rate gi. dt

in the output e. Here also, i! time constant is much greater than unity, an integrating circuit is produced, and the output voltage en becomes proportional to substantially a pure derivative oi the input voltage el. y

Fig. 5 shows a further embodiment of translating circuit'23, similar to that shown in Fig. 3, but further including a resistor'Ri connected in par- I allel with the condenser C. Upon analysis, it may be shown that by the use of this translating circuit the relationship between the output voltage eo and the input el is as follows:

It will be seen from this equation that the output voltage again is a combination of components corresponding to the input voltage and its rate of change, or time derivative. Furthermore,v by adjusting the value of resistor R1. the relative magnitudes of the control signal and rate components appearing in the output eo may be adjusted relative to one another. Thus, as the resistance value of Ri is decreased, the amplitude of the control signal component relative to the rate signal component will be increased, and as Ri is increased to a value very large compared to R, it will be seen that Equation 17 approaches Equation 15, as was to be expected.

Fig. 6 shows still another embodiment of the translating circuit 23 similar to that shown in Fig. 4, but including a resistor Ri in series with the inductance L. The output voltage from this circuit may be expressed by the equation.

and it will be seen that this equation is similar to the preceding Equation 17. However, the smaller the value of R1, the lower the magnitude of the control signal component will be, whereas the larger the value of Ri compared to R, the greater will be the relative magnitude oi the control signal component compared to the rate signal component.

` Accordingly, in Figs. 5 and 6, by making resistor R1 adjustable, there is provided a simple and effective means for adjusting the amplitude of the control signal component with respect to that of the rate signal in the output, in accordance with the requirements of the particular control system. The circuits of Figs. 3 through 6 are adapted to produce either a time derivative signal only or a combination of the control signal and rate signal. If it is additionally desired to produce a second derivative component, which might be called an acceleration signal. recourse may be had to the circuit of Fig. 7. which essentially comprises the cascaded connection ot two circuits of the type shown in Fig. 3. Thus, in the translating circuit of Fig. 7, a resistor Ri is connected in series with a condenser Ci. Across condenser C1 is connected a further series circuit comprising resistor Rz and condenser C2, and the feedback voltage e: is derived from the voltage across condenser Cz. The output voltage from the rate circuit of Fig. 2, using the translating circuit of Fig. 7, will then have the form Various conditions may be obtained from this circuit. Thus, if the time constants RiCi and RzCz are both large compared to unity, then their product must be much larger than their sum, and- 4 accordingly the first term of the right-hand member of Equation 19 becomes negligible with respect to the second term, and the system provides a pure second derivative or acceleration signal output. If one or the other of these time constants R101 or RzCz is large compared to the other, then the" Equation 19 degenerates into equation ePR-l-RzcffI- (2o) where RC is the larger time constant, from which it will be seen that the amplitude of the rate signal component depends solely upon that one of the time constants which is large, since in the ilrst term of the right-hand member o! Equation 19, the smaller time constant becomes negligible compared to the larger time constant. This, then, provides a method of adjusting the relative magnitudes of the rate signal cornponent and acceleration signal component,

which may be most simply done in practlceby e' (HR.) d l'n- Rlade (21) -which is similar in form to that ot Equation 19, and the same considerations discussed with respect -to Equation 19 apply equally well -to this Equation 21, merely substituting the time constants Ri Rs in place of the corresponding time constants R101 and RnCz of the preceding equation.

It is to -be noted that in the circuits of Figs. 7 and 8, the output comprises only rate signal and acceleration signal components, no control signal components appearing therein. To also obtain a component proportional to the control signal in the output, recourse may be had to the circuit of Fig. 9, comprising an inductance L in series with a. resistance R and capacitance C. the output voltage being derived from the voltdrop across condenser C. This output voltage may be expressed by the equation and el' a .=LC%+RC%+, (22) Accordingly, it will be seen that the magnitude of the rate component depends mainly upon the value of resistor R, the value ot the acceleration signal component depends mainly on the inductance L, and the magnitude of the control signal component relative to the other two components depends upon the value of capacitance C. By making any or all of these factors adjustable, it is possible to obtain any desired relative proportions of control signal, rate signal and acceleration signal components.

As a second method of obtaining all three signal components, the translating circuit of Fig. 10 may be used. This circuit is similar to the circuit of Fig. 7, further including a resistor Re connected in parallel with the capacitance Cz. It may be considered to be formed by cascading the circuits of Figs. 3 and 5. The eiect oi' this resistance Rs is to introduce a component in the output proportional to the control signal ei in a fashion similar to that discussed with respect to Fig. 5. The expression for the output voltage Jor the rate circuit o! Fig. 2 using this translating circuit will then be as shown in the equation and here, also, the relative amplitudes oi' the control, rate and acceleration signal components may be adjusted, by adjustment of the various resistors R1, Rz and Rs.

In a similar manner the circuits of Figs. 4 and 6 may be cascaded to also provide a combination of control, rate and acceleration signal components, relatively adjustable by simple resistance adjustments.

Also, any of the other circuits yielding rate signal components may be cascaded with similaror diiferent circuits also producing rates, for producing second and/or higher derivative signal 'components in the output e0.

Fig. 11 shows a further modication of translating circuit 23 which is adapted to produce an output signal eo similar in effect to a combined control and derivative signal, although not rigorously analytically representable as such a signal. This circuit comprises a fixed fairly high resistor R connected across the input voltage e1 in series with a variable resistor Rr, Whose resistance varies with its temperature and/or the current passing therethrough. The feedback voltage ef for the circuit of Fig. 2 is here derived from the volt-drop across thermal resistor Rt.

Suitable types of such a thermal resistor Rt are ordinary tungsten filament lamps or well-known products known by the names of thermistors or varistors. All of these thermal resistors have the property of low resistance when cold or with low values of current, and high resistance for higher temperatures or higher values of current.

Considering the condition when zero input voltage ei is impressed upon the circuit, it will be clear that no output voltage e0 and hence no feedback voltage ef will be obtained. If an input voltage el is suddenly impressed upon the circuit, this voltage will be amplied to produce voltage e0, which will be impressed across the translating circuit of Fig. 11. At .the first instant that this voltage eels impressed on the translating circuit, the thermal resistor Rt, having a low resistance compared to resistor R, will provide a very small feed-back voltage er which does not seriously decrease the net input voltage (ei-ef) to amplifier 22, so that the output voltage e0 is maintained at a high value. However, as this voltage e0 persists, the current passing through thermal resistor Rt serves to increase its resistance and thereby increase the feedback voltage ef. This decreases the net voltage input to amplifier 22, reducing the output voltage e0 accordingly, until an equilibrium condition isv reached, at which time the output voltage .eo will be materially less than its initial-value.

Accordingly, in this way, a high initial output signal strength is obtained, gradually decreasing to a lower level. This correspo-nds roughly to a combination of control signal, rate signal and acceleration signal components in the output, since 'the resulting equilibrium signal may be considered as the control signal component, and the high transient pulse initially obtained may be considered to represent a combination of the rate of change and second and/or higher derivatives of the input control signal. Thus this circuit yields at least roughly an output which may be desirably used to control a ponderable object without hunting or lag, as in Fig. 1, or for other purposes.

Fig. 12 shows a modification of the device of Fig. 11 in which a bridge circuit or four-terminal network is provided, one pair of opposite arms of which is formed by constant resistor R and the remaining opposite arms formed by thermal resistors Rt of the type discussed above. This circuit is adiusted to be substantially balanced for la very low value of input voltage e0 thereto; that is, for

10 the cold resistance values of Rt, It is to be noted that although opposite arms of the bridge are indicated as having the same resistance values, this is not at all necessary so long as the desired balanced condition may be obtained.

Accordingly, as voltage e0 varies from a small value to a large value, the output voltage er of this circuit will vary correspondingly, but with a time delay introduced by the thermal properties of the thermal resistors Rt. The effect, therefore, will be the same :as with the circuit of Fig. 11.

It is to be noted that, in each of the modications of Figs. 3 through 12 thus far described, an actual or effective derivative of the control signal Wave has been produced. However, such circuits require the transformation of the'original variable-amplitude alternating-current signal into a corresponding variable-amplitude directcurrent signal; that is, some type of phase sensitive amplifier or other detector is required, as indicated at Il in Fig. l.

In many applications, it is desirable to use variable-amplitude alternating current control signais of this type, and for purposes of economy, it would be desirable to eliminate apparatus for converting such a signal to direct-current. The circuits of Fig. 11 and Fig. 12 supply the required apparatus which eliminates the necessity for the use of phase sensitive amplifier I1. Thus, let it be supposed that the input control signal is an alternating current signal of frequency f having its amplitude modulated in accordance with the control signal ei discussed withl respect to Figs. 3 to, 9. Accordingly, this input signal may be expressed as el sin 21rft. If such a signal is suddenly impressed -upon the yrate circuit of Fig. 2, using the translating circuit of Fig. 11, the effect will be the same as already described with respect to Fig. 1l, since the thermal lag of the thermal resistor Rt will prevent its following the rapid fluctuations in the instantaneous value of the input voltage at the frequency f, so that the system will respond effectively only to the changes in the modulation envelope el of the input signal. Accordingly the output signal derived will be of the form e0 sin 21rft, where eo now represents the combination'of control and derivative components of the input signal modulation envelope ei, as is desired.

The circuit of Fig. 12 will also serve to provide an output from the circuit of Fig. 2 of the same frequency f but having a modulation envelope which is a combination of the modulation envelope el of the input signal eixsin 21rft and its derivatives.

Fig. 13 shows a further form of translating circuit useful with Fig. 2, i-n which the necessity for the phase sensitive amplier I1 is also eliminated. As indicated schematically in Fig. 13, this translating circuit consists of a suitable single-frequency pass-filter circuit passing fre- ,ouency f, whose loss vs. frequencyV characteristic in the neighborhood of the pass frequency f is substantially linear, as indicated in Fig. 13. If such a translating circuit is included to the feedback path of the rate circuit of Fig. 2, a large amount of feedback will be obtained for the components of the input signal e0 sin 21rf having frequency f, so that if a steady signal ofd frequency f is applied to the input of the rate circuit sub@ f, in a manner similar to suppressed carrier amplitude modulation, which sidebands will be transmitted through the translation circuit 23 of Fig. 13 in inverse relation to their frequency departure from the frequency f. Thus, a sharp change in the magnitude el of the input signal elXsin 21rft will effectively produce sidebands having Wide separation from the carrier frequency f, which will thereby be only weakly transmitted through the filter circuit of Fig. 13 to produce relatively low feedback er and corresponding high output eo, as is to be desired.

In this manner the circuit operates to produce an alternating rate signal output from an alternating input signal; that is the present circuit serves to differentiate the modulation envelope of the input signal and to produce an output which consists of the same carrier modulated by this derivative,

also be desirable to produce various integrals ofthe input signal, such as to correct for persisting errors, and forA other uses. the feedback circuit or translating circuit 23 should be of a character inverse with respect to the over-all desired characteristic. Therefore to produce an over-all integration, it would appear necessary to provide differentiating circuits for the translating circuit 23.

Such is actually the case, and such feedback or translating circuits for producing over-al1 integrating effects are shown in Figs. 14 to 22. These circuits are essentially the inverse circuits of the circuits of Figs. 3 to 13 and will not be discussed in great detail.

Fig. 14 shows a series-connected condenser C and resistor R energized by the feedback-input signal en. The feedback voltage derived l from across resistor R produces a, resultant output signal eo having components proportional to the input signal and the time integral thereof. The relative amplitudes of the control signal and integral signal components of the output may be adjusted by adjustment of the values of condenser C or resistor R. It will be seen that the circuit of Fig. 14 is essentially a differentiating circuit of a. well-known type, as shown in the above mentioned Hull patents.

Fig. 15 shows a feedback circuit consisting of a series connected-resistor R and inductance L, the feedback voltage er being obtained as the voltdrop across inductance L. The output voltage en will be similar to that of Fig. 14, and may be similarly adjusted.

Fig. 16 shows a feedback circuit consisting of series-connected resistor R and primary winding P of a. transformer T having mutual inductance M, the feedback voltage being derived from the secondary winding S of transformer T. Here again, the output voltage e0 will be of the same character as with Figs. 14 and 15. For high values of resistor R relative to mutual inductance M, a substantial pure integral output will be obtained.

Fig. 17 shows a feedback circuit which is essentially the cascaded connection of two circuits of the type of Fig. 14, and as a result produces an output voltage en having components corresponding to single and double time integrals of the input voltage, which are also relatively adjustable in magnitude by adjusting the various circuit constants.

Fig. 18 represents a feedback circuit having the As discussed above,

12 cascaded connection of two circuits of the type of Fig. 15, and the output voltage e will be of the same type as in Fig. 17.

Fig. 19 shows a feedback circuit comprising series-connected condenser C. resistor R and inductance L, the feedback voltage er being derived from the volt-drop across inductance L. The resultant output voltage es using this circuit will have components representing the control signal ei and the single and double time integrals thereof.v

Fig. 20 shows a circuit which is essentially the inverse of that of Fig. 11. In this instance, a sudden change of input voltage er will produce a corresponding change of output voltage eo which at the first instant will produce a large feedback voltage e1 causing only a small output voltage e0. As resistor Ri gradually heats up and increases its resistance the feedback voltage slowly decreases, permitting the gradually increasing of output voltage eo corresponding roughly to a time integral of the input signal ei.

The circuit of Fig, 21 is essentially the inverse of the circuit of Fig. 12. In this instance, the bridge circuit is adjusted to be balanced when the thermal resistors Ri are in their heated or high resistance condition. Accordingly, when a signal is iirst impressed upon this circuit the bridge will be widelyunbalanced, producing a large feedback voltage and a consequent low output voltage es. As the input voltage is maintained, 1 the resistors R: gradually heat up and slowly bring the bridge circuit back toward a bal-v anced condition, reducing the feedback voltage correspondingly. This gradually increases the output voltage e0 in a corresponding sense, producing an output voltage which roughly represents a time integral of the input voltage.

It is to be noted that the circuit of Figs. 20 and 21 will also operate with modulated alternating signals in which the control signal ei is effectively a modulation upon a carrier of frequency f, the input to the circuit being of the form ci sin 21rft. In this case, as in Figs. 11 and 12, variations at the carrier frequency f are ineective, due to the thermal lag of the resistors Re and accordingly the output voltage will have a modulation envelope er which corresponds directly to and to a time integral of the modulation envelope ei of the input voltage.

Fig. 22 represents the inverse of Fig. 13. Here a lter circuit is used as the feedback circuit having high loss at the carrier frequency f. yThis illter is in effect, therefore, a single-frequencyelimination filter, ofA which many types are well known in the art. For a sudden large change in input voltage Asidebands widely separated in frequency from the carrier frequency f will be produced, which will be only slightly attenuated by the filter circuit to produce a large feedback voltage, holding the output voltage to an initial low value. As the change in signal decreases and ceases, these sidebands approach the carrier frequency, producing smaller feedback voltage and larger output voltage, so that the modulation envelope of the output eoxsin 2rft corresponds to the time integral of the modulation envelope of the input eixsin 21rft, the carrier frequency f' Y3-22. As has just been seen, this instantaneous gainumay be of such character as to provide an integral functional relationship, a. derivative relationship or any other desired relationship, between the input and output voltages e and e: of the translating circuit 23. The voltage eo does not depend in any way upon the gain a of ampliiler 22. Since p. is generally very small and less than 1, being normally of the order of 0.1 to 0.001 in value, it will be seen that the present circuit in Fig. 25, the output oi amplifier 22' may actuate a suitable torque `motor 32 which controls a hydraulic valve 23 for producing a differential would then beor the hydraulic type. In order to derives an output derivative or integral of ampli-A i ned magnitude which is substantially independent of the amplifying characteristics of ampliiler 22, depending only upon the characteristics of translating circuit 23, the over-all gain being or no fluctuation in characteristics, so that theA signal-modifying circuit of Fig. 2 will have greatly improved operating characteristics over that described with respect to Fig. 1.

It is to be understood that the device of Fig. 2 may be used to obtain any desired type of functional relationship between an output voltage e and an input voltage ei, merely by using a translating circuit 23 having an inverse functional relationship between its input and output voltages, and that thereby the overall characteristics cf the circuit will be substantially independent of the amplifier 22 and dependent only upon the characteristics of the translating circuit 23.

Combined derivative and control signal output4 may be obtained by using the feedback circuits of Figs. 3-12. Combined integral and ,control signal output may be obtained by using the feedback'circuits of Figs. 14-21. Any other desired relationship may be obtained by using a proper feedback circuit determined by the considerations discussed above.

It is to be understood that amplifier 22 need input signal 'el is fed to an electronic amplifier 22' whose output energizes the field winding 0f a suitably driven generator 26. The output voltage of the armature 21 of generator 26 may then be used to control the servo 2| of Fig. 1, and is also used to provide the voltage eo which is fed back vthrough translating circuit 23' to produce the feed-back voltage er to be combined with the input voltage ei.

Another type of system is shown in'Fig. 24 wherein the output of amplifier 22' correspondingly actuates a variable speed motor 28 driving a generator 29 whose output may be used l to control servo 2 I A pick-up coil 3i may be associated with generator 29 to produce a, voltage.

corresponding to the output of generator 29, and this voltage may then be used as the input e0 to translating circuit 23 to provide the feed-back voltage er.

The amplifying device 22 need not even be wholly electrical in character. Thus, as shown provide the feed-back signal, a pressure pick-off 34 may be used .to generate a signal correspondlng to .the differential pressure applied to the servo 2| and this signal .is then fed to the translating circuit 22' to provide feedback voltage for amplifler`22'. l'

Many other types ofsystem, including electrical, mechanical, hydraulic, pneumatic, thermal, etc., amplifying and servo-controlling a devices may be used for amplier 22 of Fig. 4. As shown above. the overall characteristics of the improved rate circuit of the present invention depend only upon the characteristics of the translating circuit 23, so long as the gain fof the amplier 22 is much greater than the attenuation of the translating circuit 23. Y

Fig. 26 shows a complete control circuit, such as.for the system of Fig. 1, which incorporates and combines both a phase-sensitive amplier anda rate circuit of the type discussed with respect to Fig. 2. .Here the input signal, which' is of the variable-amplitude. reversible-phase alternating type, such as derived from the pickoif I3 of Fig. 1, is connected to the primary of an input transformer 38 having two independent secondary windingsv 31 and 38. In order to pro- .put voltages to tubes 4| and 42 are connected in series with respective oppositely-varying feedback voltages produced, as will be described, across condensers 43 and 44.

Impressed between ground and the interconnected cathodes 46 .and 4`| of the respective tubes 4I and 42 is a source of alternating current 48 having the same frequency as the frequency of the input signal and having xed phase with respect thereto. Preferably this phase relationship is so chosen that the voltage of source '48 is always either in phase coincidence or inphase opposition with the input signal voltage, depending upon the phase-sense of this input.

The anodes 5l and 52 of tubes 4l and 42 are connected to ground 48 through respective output resistors 53, 54, and hence are energized by source 48. The screen grids 50, 51 are connected together and to ground throughs. voltage-dropping resistor 5l.

Neglecting for the moment the eiect of the feedback voltages across condensers 43, 44, tubes 4i, 42 are selected and adjusted to produce'equai voltages across resistors 53, 54, for zero input signal voltage to transformer 36. These voltages across resistors 53. 54 will be uni-directional pulsating voltages produced by the half-wave rectication of the voltage of source 4B in tubes 4I, 42.

15 Accordingly, the net voltageacross anodes 5|, 52 will be aero under these conditions.

When a. signal of predetermined phase is impressed on input transformer 38, one of the control grids 38 or 48, for example, grid 33 will become more positive at the same instant that its corresponding anode becomes positive, whereas the other grid 48 will become more negative as its corresponding anode 52 becomes positive, by virtue of the opposite connection of the secondaries 31,38 to these respective grids 33, 48. It will be clear that the particular grid 38 or 40 which thus becomes more positive will depend upon the particular phase-sense of the input control signal, which may reverse, depending on the control action required.

Assuming. that grid 39 is thus rendered more positive, more anode current will flow to anode 5| during negative half cycles of source 48 (when anodes 5|, 52 are positive with respect to their cathodes 46, 41) and therefore a greater voltage will be impressed across its corresponding output resistor 53. At the same time, the other tube 42 whose control grid 43 becomes more negativewill have reduced anode current, and accordingly a reduced volt-drop will be produced across its corresponding output resistor 54. The net voltage across the series-connected resistors 53, 54 (that is, the voltage across anodes 5|, 52) will then be a half-wave rectified pulsating voltage having a magnitude corresponding to the amplitude of the alternating input control vsignal and having a polarity corresponding to the phase of this input signal.

It will be seen therefore that tubes 4|, 42 comprise essentially a phase-sensitive amplifier or detector such as indicated schematically at I1 in Fig. 1. At the same time, however, tubes 4|, 42 are adapted to be used as the amplifier 22 of Fig. 2. Thus, the output voltage derived across anodes 5|, 52 is applied to a translating circuit 23 to produce corresponding oppositely varying feedback voltages across condensers 43, 44, which are inserted in series with respective secondary windings 31, 38 of transformer 36 to control the input grids 39, 48 of tubes 4|, 42 in the manner discussed with respect to Fig. 2 and the subsequent iigures.

Feedback circuit 23, in this instance, comprises a pair of resistors 6|, 62 connected to respective anodes 5|, 52 and joined in series with a condenser 63 and a further resistor 64. Because of the balanced circuit arrangement, condenser 63 and resistor 64 are essentially equivalent to (that is, will have the same effect as) the circuit shown in dotted lines, comprising a resistor 66 in series with a condenser 61, and a resistor 68 in series with a condenser 69, the junction point of condensers'61 and 69 being at the same potential as the `iunction point 45 of condensers 43, 44 (that is, half-way between the potentials of anodes 5|,

52) so that it may be joined thereto as indicated,`

if desired. If each of the resistors 86, 68 has a resistance half that of resistor 84 and if each of 16 corresponding to the input control signal and its time integral. The effect of series resistors. such as 68 and 88, is to increase the relative magnitude of the control signal component and to generally extend the range of rates of change of the input signal which can be effectively handled by the system.

'I'he output voltage d erived across condenser 63 and resistor 64 (which is twice the hypothetical voltage across resistor 68 and condenser 81, for example) is then impressed upon a second push-pull integrating circuit, such as of the type shown in Fig. 5. which thereupon produces across condensers 43 and 44 oppositely varying output voltages corresponding to the voltage across condenser 63 and resistor 84 and first and second time integrals thereof. Accordingly. this net output voltage has components corresponding to the difference between the anode voltage oi' tubes 4| and 42 and to time integrals thereof. These output voltages, which are varying unidirectional y voltages, are -added to the alternating control the condensers 61, 88 has a capacitance twice As discussed with respect to Fig. 3, that circuit will produce an output voltage having components signal voltages produced in secondaries 31, 38 to control tubes 4|, 42.

In essence, the negative biases on tubes 4|, 42 are controlled in opposite-senses by the feedback circuit 23. As described relative to Fig. 2, this will produce a unidirectional differential voltage having control signal. rate signal and second derivative signal components, across resistors 53, 54, so long as the gain of tubes 4I, 42 is large compared to the attenuation of circuit 23. This voltage is then differentially impressed upon the Iinputs to respective push-pull connected modulator tubes 1I, 12 having an alternating voltage derived from source 48 impressed upon the anodes 13, 14 thereof through respective halves of the primary winding of 'output transformer 83, and also upon the screen grids 16 and 11 through a voltage-dropping resistor 18. Source 48' is shown as independent from source 48, but is preferably identical therewith, or at -any rate produces a voltage of a phase and frequency identical with that of source 48. A suitable cathode biasing resistor 19 is connected be` tween the cathodes 8|, 82 and ground 48.

In the absence of input signal to transformer 36, as stated above, equal half-wave rectified voltages wi1l be produced across resistors 53, 54. When a. definite control signal is impressed upon the input to transformer 36, for example, such as to render grid 39 more positive and grid 48 more negative during negative half cycles of source 48, the voltage across resistor 53 will increase and that across resistor 54 will decrease, as discussed above, in accordance with the magnitude and the derivatives of the magnitude of the input voltage. These voltages are also unidirectional half-wave rectied voltages, since tubes 4I, 42 will be conductive' only during the half-cycles of source 48 when negative voltage is impressed on cathodes 46, 41. Being unidirectional, they must be directly applied to grids 18, 15 to control tubes 1|, 12 in the desired manner. Because of this direct connection, the cathodes 8|, 82 are directly connected to ground at 49, through biasing resistor 19, so that anodes 13, 14, energized from source 48' must have instantaneously opposite polarity from that of anodes 5|, 52 if sources 48 and 48' are to be the same, l Tubes 1i, 12 can conduct only when positive voltage is applied to anodes 13, 14.

as is preferable.

blocked and zero voltage would -appear across resistors 53, 54. Hence tubes 1|, 12 would be ineffective and no output could be obtained, since tubes 1|, 12 could operate only at times when they would have zero input.

To avoid this, condenser 59 is connected across anodes 52 and hence across resistors 53 and 54 in series. Condenser 59 serves two functions simultaneously. Firstly, it carries over" the output voltages of tubes 4|, 42 from the positive half-cycle (when anodes 5|, 52 are positive rela.- tive to cathodes 49, 41) to the succeeding halfcycle, by being charged during the positive half cycles and remaining substantially charged during the succeeding half cycles, so that the proper input voltages are applied to tubes 1|, 12 during the periods in which these tubes are effective.

Condenser 59 serves the additional function of eliminating the high bias caused by the standby or quiescent voltage across resistors 53, 54 by carrying over only the difference between the volt-drops across resistors 53, 54. Thus. during the conducting half cycles of tubes 4|, 42, considerable current is drawn through resistors 53, 54, rendering grids 19, markedly negative, perhaps beyond cut-off. If these voltages were carried over, as by condensers individually shunted across resistors 53, 54, excessive bias would remain on grids 19, 15 and would seriously impair the operation of tubes 1|, 12. However, condenser 59, being connected across anodes 5|, 524, is charged up by the difference in these voltages. During the succeeding half-cycles of opposite polarity, tubes 9|, 42 are blocked by the negative voltages applied to their anodes 5|, 52 and condenser 59 discharges slowly through resistors 53, 54 in series. These resistors 53, 54 thereby serve as voltage dividers and impress only half the voltage of condenser 59 (which is the desired output voltage) on each of grids 19, 15, thus eliminating the excessive biases discussed above.

Accordingly, anode currents will be produced by tubes 1|, 12 whose difference will correspond to the difference between the volt-drops across resistors 53, 54 and hence to the magnitude and time derivatives of the control signal input t0 transformers 36. These currents are again halfwave-rectied pulsating currents, since tubes 1|, 12 conduct only half the time. These currents are then fed diierentially into the respective halves of the primary of center-tapped output transformer 83. A condenser 94 may be connected across the primary of transformer 33 to pr'oduce a ily-Wheel circuit for supplying the missing half-cycles of the output voltage. 'I'he condenser 94 preferably tunes transformer 89 to the frequency of source 49'. The output voltage derived from transformer 93 can then be used to suitably control any type of servo 2| (Fig. l), which may be a two-phase motor having one of its two-phase windings xedly energized from a source in phase quadrature with source 49 and the other winding controlled from the output of transformer 93, or may comprise any other type of servo, such as one which may be controlled from a torque motor 99, comprising two opposed coils 81, 89 fed from respective halves of the secondary or transformer 83 through source 99 in 18 weak control signal, or, generally, for producing an alternating voltage whose magnitude has components corresponding to the magnitude of an alternating control signal and to time derivatives thereof. Such circuits are very useful in servo systems and automatic pilots. By proper choice of values of the circuit components of feedback circuit 23, any desired relative magnitudes of the control signal. rate signal and other derivative components of the currents controlling servo 2| may be adjusted to the proper value for substantially eliminating all hunting and lag.

Fig. 27 shows a modification of the circuit of Fig. 26. Here the input control signal ls supplied to input transformer 39 as before, and the voltages obtained in secondary windings 31, 33 are led to the control grids 39' and 49' of phase-sensitive amplifier or detector tubes 4|' and 42' by way of series-connected grid Aresistors 9| and 92, and in series with the feedback voltages produced across condensers 43' and 44' in the manner to be described. Cathodes 45' and 41' of tubes 4|' and 42' are connected together and to4 ground at 49. Anodes 5|'. 52 of these tubes are connected through respective output resistors 53. 54 to source 49 of alternating current. The action of tubes 4|', 42' is exactly similar to that of tubes 4|, 42 of Fig. 26 and supplies differentially-varying lhalf-wave-rectified unidirectional voltages to the control grids 93, 94 of the succeeding A. C. energized D. C.'ampliiler tubes 99, 91, the difference in these voltages corresponding in polarity and magnitude to the phase-sens and magnitude of the signal input to transformer 39 (neglecting for the moment the effect of feedback circuit 23') Condenser 59' is connected between anodes 5|' and. 52' and serves the same function as condenser 59 of Fig. 26. Cathodes 99 and 99 of tubes 99, 91 are connected together and through a common cathode biasing resistor |99 to the junction of resistors 53 and 54 and to source 49. The screen grids |9| and |92 of tubes 93, 91 are connected together through a voltage-dropping resistor |93 to ground at 49. The suppressor grids of tubes 95. 91 are connected to their cathodes in the conventional manner. The anodes |99, |91 of tubes 95, 91 are connected through respective output resistors |93. |99 to ground at 49. Condenser |94 is connected across anodes |95, |91 and serves the same function as condensers 59' and 59. In this manner. tubes 4|'. 42 and 99, 91 form a two-stage alternating-current-energized phase-sensitive detector and ampliiler.

The resultant voltage appearing across condenser |94 is then connected to the input of feedback circuit 23. which is similar in function to circuit 23 of Fig. 2 and Fig. 26, and serves to produce across its output condensers 43 and 44 oppositely varying voltages corresponding to the magnitude and time integrals of the output voltage across condenser |94. These voltages are inserted in series with the respective inputs to tubes 4|'. 42 and effectively serve to control the bias of tubes 4|', 42' to thereby control the amplication of the alternating signals fed to these tubes by way of transformer windings 31. 39.

Feedback circuit 23' is generally similar to circuit 23 of Fig. 26, with certain modifications for improving the operation thereof. Here also a balanced push-pull type circuit is used for producing equal and oppositely varying output voitages across condensers 43', 44' for introduction' 19 into the input circuits of tubes 4|' and 42' in opposite senses.

The feedback circuit 23 may best be explained by considering only one half of this circuit (which is duplicated in opposite sense for the other half) and hy first assuming that resistors ||1 and I I0 to have high resistance values, so z be a substantially pure double integral, which produces a resultant output voltage eo from the entire circuit which will be a substantially pure second derivative of the input signal ei, which in this instance is the magniture of the input voltage to input transformer 38. Resistor IIS may be, made adjustable `to adjust the magnitude of the second derivative component thus obtained.

The insertion of a slight amount of adjustable resistance ||1 in series with condenser IIS will cause the voltage across the series connection of resistor |I1 and condenser IIB to have components corresponding to the input voltage to the feedback circuit directly, and to the time integral of this input voltage. This combined voltage is then integrated by the second integrat ing circuit IIB-42|, and will therefore produce a combination of the single and double integrals in the feedback circuit output. Since resistance III is vry large. the current in the feedback circuit will be substantially proportional to the input voltage to the feedback circuit, and aclcordingly by adding a small amount of resistance at IIB, the volt-drop thereacross will be proportional to the feedback circuit input signal. Hence, thev resultant output voltage across the series connection of resistor IIB and condenser |2| will have components directly corresponding to the input to the feedback circuit and to the irst and second time integrals thereof, and will therefore be of the character required to produce control signal, rate signal and time derivative signal components in the resultant output voltage appearing across condenser |04, in the manner already described.

Variable resistance ||3 taken in cooperation with xed resistors III and ||2 forms a voltage divider across condenser |04, and thereby provides means for controlling the magnitude of the input to the feedbackcircuit 23.

The remaining half of the feedback circuit 23 is exactly similar to that just described but connected in reverse sense, so that the voltage appearing across condenser 44' will be exactly of similar wave form to that across condenser 43 but of opposite polarity and thereby serve to control tube 42' in a sense opposite to that of 4|' to yield the required differential output from the complete circuit.

Condensers 43' and 44 provide respective low impedance connections between the windings 31, 38 and ground at 4'9, in order to prevent the building up of substantial voltage of the fre-- It will be noted that the voltage input to feed-- back circuit 23' is derived after two stages of amplification, first by tubes4|', 42' and then by 83, 01. The resulting voltage-may produce too large an output from circuit 23', thereby providing 4excessive bias for grids 33', 40'. To overcome this effect, a further bias is supplied from source 48 by way of rectifier |3I. Thus, connected across resistor ||3 is a potentiometer |32, whose variable arm |33 is connected to rectifier |3I. Rectifier |3| will be seen to have two load circuits, the iirst comprising the upper part of potentiometer |32, resistor III, and resistor |09 to ground. and the other comprising the lower part of potentiometer |32, resistor I|2 and resistor |08 to ground. Each of these load circuits is bypassed to ground for alternating currents by acondenser |34.

The unidirectional voltage drops thus produced across the respective parts of potentiometer |32 are further filtered by condensers 43', 44' and are thereby applied to the control grids 39', 40' to supply the proper net bias thereto.

In this manner, in accordance with the theory discussed with respect to Fig. 2, the voltage produced across condenser |04 contains components proportional to the input control signal and yto time derivatives of the various orders thereof. This combined signal is fed to a further amplifier circuit comprising tubes |38, |31 which have their anodes |38, |39 energized by A. C.` by being connected to source 48 through the torque motor coils 81, 88, the cathodes of tubes |36, |31 being connected together and to ground through the common/biasing resistor |4I. Each of the windings 81, 88 is bypassed by respective bypass condensers ISI, |52, whereby substantially only direct current passes through these windings.

For zero voltage input to transformer 38, the currents passing through coils 81, 88 will be equal and will have opposite effect on the output of torque motor 88. When a xed or varying signal is impressed on transformer 38, the currents passing through windings 81, 88 will vary equally and' oppositely in accordance with this input signal and its time derivatives, whereby the output of torque motor 88 may be utilized, with the proper proportioning of these signal components, to suitably control a servo such as 2| of Fig. 1 for actuating a pondera-ble object without hunting or lag as is desired.

Fig. 28 shows a further modification of the circuits of Figs. 26 and 2'? employing a phasesensitive detector stage 4|, 42 similar to that of Fig. 26 and a single amplifier stage '98, 91 similar to that of Fig. 27. The feedback circuit is similar to circuit 23 of Fig. 27, but is connected in this instance across the torque motor 81, 88 which forms the output of tubes ISli, l91. The rate circuit action of this modification is believed to be clear from the preceding explanation.

YIn this instance, rectifier |3| is omitted, and the proper bias obtained by utilizing the grid rectifying properties of tubes 4|, 42. For this purpose, the cathodes of tubes 4|, 42 are connected to A. C. source 48" of the same phase as source 48 but of lesser amplitude, thus providing proper bias. The proper balancing action is obtained by adjustment of potentiometer |40,

whose variable arm is grounded. The remaining portions of Fig. 28 are similar to Figs. 26 and 21 and are believed to require no further explanation.

As many changes could be made in the above construction and many apparently widely difgaat 2i ferent embodiments of this invention could be made without`departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimedis: Y

' 1. In a control system for a ponderable object having means for producing a reversible-phase, variable magnitude alternating control signal corresponding to the desired motion of said object and also having a servo system for moving said object, the combination comprising balanced two-channel electronic means for amplifying said signal and producing therefrom' a reversiblepolarity, variable-magnitude, unidirectional output signal, balanced circuit means responsive to said output signal for producing therefrom oppositely varying unidirectional feed-back signals respectively having components corresponding to the magnitude of said unidirectional signal and to at least one time integral thereof, the ampliilcation of said amplifying means-being much larger than the attenuation of said circuit means, means for .oppositely and degeneratively controlling the amplication of said two channels by said respective feed-back signals, and means for controlling said servo system by said output signal, whereby said servo system may be controlled in accordance with said control signal and at least one time derivative thereof.

2. In a.v control system for a ponderable object having means for producing a reversible-phase variable-magnitude alternating control signal corresponding to the desired motion of said object, the combination comprising balanced twochannel electronic means for amplifying said signal and producing therefrom a. reversible-polarity variable-magnitude unidirectional output signal, balanced circuit means `responsive to said output signal for producing therefrom oppositely varying unidirectional feed-back signals respectively corresponding to at least one time integral of the magnitude of said output signal, and means for oppositely controlling the amplification of said two channels by said respective feed-back signals, whereby said output corresponds to at least one time derivativel of the magnitude of said control signal.

3. In a control system for a ponderable obiect having means for producing a control signal corresponding to the desired motion of said object.

the combination comprising means for amplifying said control signal, means for integrating the output of said amplifying means, and means for opposing said control signal by said integrated signal in the input to said amplifying means, whereby said output corresponds to the rate of change of the magnitude of said control signal.

4. In a control system for a ponderable object having means for producing a control signal corresponding to the desired motion of said object and also having a servo system for moving said object, the combination comprising means for amplifying said signal, capacitance-resistance circuit means responsive to the output of said amplifying means for producing a feed-back signal having components corresponding to said control signal and at least one time integral thereof, the gain of said amplifying means being large compared to the attenuation of said circuit means, means for degeneratively controlling said ampli- :lier by said feed-back signal. and means for controlling said servo system by said output, whereby said servo system is controlled in accordance with 22 said control signal and at least one time deriva tive thereof to produce non-hunting, non-lagging actuation of said ponderable object.

5. In a control system for a ponderable object having means i r producing a control signal cor responding to the desired motion of said object and also having a servo system for moving said object, the combination comprising means for amplifying said signal, circuit means responsive to the output of said amplifying means for producing a feed-back signal having components corresponding to said control signal and to at least one time integral thereof, the amplification of said amplifying means being large compared to the attenuation of said circuit means, means for controlling the input of said amplifying means by the difference between said control signal and said feed-back signal, and means for controlling safd/ servo system by said output, whereby said servo'system is controlled in accordance with said control signal and at least one time derivative thereof.

6. In a control system for a ponderable object having means for producing a control signal corresponding to the desired motion of said obiect, the combination comprising means for amplifying said signal, circuit means responsive to the output of said amplifying means for producing a feed-back signal corresponding to at least one time integral of said output, and means for controlling the input of said amplifying means by said feed-back signal, whereby said output corresponds to at least one time derivative of said control signal.

7. In a control system for a ponderable object having means for producing a control signal corresponding to the desired motion of said object and also having a servo system for moving said object, the combination comprising means for amplifying said signal, circuit means for modifying the output of said amplifying means to produce a feed-back signal therefrom, the amplification of said amplifying means being large compared to the attenuation of said circuit means, means for degeneratively coupling said feed-back signal to the input oi' said amplifying means, and means for controlling said servo system by said l output, whereby said servo system is controlled in accordance with said control signal modined in inverse manner to the modification produced by` said circuit means.

8. In a control system for a ponderable object having means for producing a control signal corresponding to the desired motion of said object and also having a servo system for moving said object. the combination comprising means for amplifying said signal, circuit means for modifying the output of said amplifying means to produce a feed-back'signal and for coupling said feed-back signal to the input of said amplifying means, and means for controlling said servo syscontrol signal modified in inverse manner to the modification produced by said circuit means.

10. In a control system responsive to' a controi signal, the combination comprising means for amplifying said control signal, means for modifying the output of said amplifying means to produce a modified signal. the amplification of said amplifying means being much larger than the attenuation of said modifying means, and means for degeneratively controlling said amplifying means by said modied signal, whereby said output corresponds to said control signal modified in inverse manner to the modification produced by said modifying means.

1l. A control system as in claim 10, -wherein said modifying means comprises means for integrating said output, whereby said output corresponds to a time derivative of said control signal.

l2. A control system as in claim 10, wherein.

said modifying means comprises means for producing a signal corresponding to said output and a time integral thereof, whereby said output corresponds to said control signal and a time derivative thereof.

13. A control system as in claim l0, wherein said modifying means comprises means for producing a feed-back signal corresponding to said.

a feedback path from said output circuit to said input circuit and including circuit means for producing a feedback voltage having a component corresponding to a time integral of the output voltage from said amplifier, said feedback path being connected to apply said feedback voltage in a degenerative sense to said input circuit, whereby said output voltage has a component representing a time derivative of said input voltage. f

18. An amplifier adapted to deliver an output voltage having a component corresponding to the voltage input thereto modified with respect to time, said amplifier comprising an input circuit and an output circuit, a feedback path from the output circuit to the input circuit, and a reactance in said feedback path to provide a feedback 'voltage corresponding to the output voltage modifled with respect to time, said feedback path being connected to apply said feedback voltage in a degenerative sense to said input circuit.

circuit to the input circuit, and a resistor and a capacitor serially connected across said output circuit, said capacitor also forming a part of said feedback path to provide a feedback voltage to said input circuit modified with respect to the output circuit voltage, said feedback path being connected to apply said feedback voltage in a degenerative sense to said input circuit.

15. In a control circuit responsive to an input voltage, the combination comprising an amplifier having an input circuit and an output circuit, a feedback path from said output circuit to said input circuit, resistor means and capacitance means serially connected to said output circuit. said capacitance means and a portion of said resistance means also forming a part of said feedback path to provide a feedback voltage to said input circuit which is modified with respect to said output circuit voltage, said feedback path being connected to apply said feedback voltage in a degenerative sense to said input circuit.

16. A differentiating amplifier adapted for delivering an output voltage having a component corresponding to a time derivative of an input voltage comprising an amplifier having an input circuit and an output circuit, a feedback path from said output circuit to said input circuit, resistance and capacitance means connected to said output circuit and including a parallel-connected resistor and capacitor forming a part of said feedback path to provide a feedback voltage to said input circuit having components corresponding to said output voltage and at least one time integral of said output voltage, said feedback path being connected to apply said feedback voltage in a degenerative sense to said i'nput circuit,

17. In a control circuit responsive to an input voltage, the combination comprising an amplifier having an input circuit and an output circuit,

I 19. In a control system including means for producing a control signal and servo mechanism controlled thereby for moving an object, the combination comprising means for amplifying said signal and applying it across output taps, feedback circuit means connected across said output .taps and including means for modifying the output of said amplifying means to produce a feedback signal therefrom, the amplification of said amplifying means being high compared to the attenuation of said circuit means, means for degeneratively coupling said feedback signal to the input of said amplifying means, and means for controlling said servo mechanism with the output of said amplifying means.

Y 20 In a control circuit of the character described, an amplifier having an input and an output, the voltage output of said amplifier being connected across said output, a feedback path connected across said output and connecting with said input, said feedback path including circuit means for producing a feedback voltage having a component corresponding to a time integral of the output voltage of said amplifier, and said feedback voltage being applied in a degenerative sense to said input, whereby the output voltage includes a component corresponding to a. time derivative of the input voltage.

21. In a control circuit of the character described, an amplifier having an input and an output, the voltage output of said amplifier being connected across said output, a feedback circuit connected across said output and connected to said input, and a reactance in said feedback circuit for providing a feedback voltage component corresponding to the voltage applied to said feedback circuit modified with respect to time, said feedback voltage being supplied in a degenerative sense to the input.

22. A differentiating amplifier for supplying an output voltage having a component corresponding to a time derivative of the input voltage, said amplifier having, an input and an output, the voltage output of said amplifier being connected across said output, a feedback path connected across said output and connecting with the input. and resistance and capacitance means connected in series and across said output, said capacitance means being also included in said feedback path andsaid resistance and capacitance means being of such values as to provide a feedback voltage component corresponding to' the time integral of the voltage supplied to said anat 25 feedback path, said feedback voltage being supplied to said input in a degenerative sense.

23. In a control circuit of the character described, -an amplier having an input and an output, the voltage output of said amplifier being connectedacross said output, a feedback path connected across said outputand connecting with said input, inductance and resistance means connected in series and across said output, said resistance means at least in part being included in said feedback path, said resistance and inductance values being such as to provide a feedback voltage componentcorresponding to the voltage applied to said feedback path modified with respect to time, and said feedback voltage being applied in a degenerative sense to the input of said amplifier.

24. In a control circuit of the character described, an amplier having an input and an output. the voltage output of said amplifier being applied across said output, a feedback path connected across said output and connecting with said input, a rst, series connected, resistance and inductance means connected across said output and a second, series connected, resistance and inductance means connected across one of said first mentioned resistance and inductance means, and one of said last mentioned resistance and inductance means supplying a feedback voltage, said resistance and inductance means being of such values as to provide a feedback voltage component corresponding to the output voltage of said amplifier modified with respect to time, and said feedback voltage being supplied to said input in a degenerative sense.

25. In a circuit of the character described, an amplifier having an input and an output, a feedback path from said output to said input, resistance and inductance means connected to said output and in part being included in said feedback path, the values of said resistance and inductance means being such as to supply a feedback voltage component corresponding to` the voltage applied to said feedback path modified with respect to time, and said feedback voltage being supplied to the input in a degenerative sense.

26. In a circuit of the character described, an amplifier having an input and an output, a feedback path from said output to said input, resistance and inductance means connected in series and across said output. and a second resistance and inductance means connected in series and across said first mentioned resistance means to provide a feedback voltage component, said feedback voltage component being derived from said second mentioned resistance means and being applied in a degenerative sense to the input of said amplifier.

27. In a circuit of the character described, an

amplifier having an input and an output, a feedback path from said output to said input, means including inductance, resistance and capacitance connected in series and with\ said output, said capacitance means lbeing included in said feedback path, and all of said means being of such values as to supply a feedback voltage including components proportional to the voltage applied to said feedback path and to a modification thereof with respect to time, said -i'eedback voltage being applied to the input in a degenerative sense. 28. A circuit of the character recited in claim 23. in which the resistance and inductance means are so constructed and relatively arranged in circuit as to supply a feedback voltage component approximating a time integral of the voltage supplied to said feedback path.

29. A circuit of the character recited in claim 25, in which the resistance and inductance means are so constructed and relatively arranged in circuit as to supply a feedback voltage component approximating a time integral of the voltage supplied to said feedback path.

30. A circuit of the character recited in claim 27, in which the inductance, resistance and capacitance are so constructed and relatively arranged in circuit as to supply a feedback voltage including components proportional to the voltage applied to said feedback path and to a time integral thereof.

JEFFERSON R. WILKERsoN. REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Jones June 20, 1944 Certificate of Correction Patent No. 2,448,564. September 7, 1948.

JEFFERSON R. WILKERSON It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 7, line 16, Equation 18, for e+ read -e=; column 8, lines 15 and 39, Equations 21 and 22, for e.,=" read. -e=;

and that the said Letters Patent should be rea.d with these corrections therein that the same may conform to the record of the case m the Patent Oflce.

Signed and sealed this 26th dey of April, A. D. 1949.

[SEAL] THOMAS F. MURPHY,

Assistant Oammzasoner of- Patents. 

